Advanced fiber-optic communication systems using a wavelength division multiplexing (WDM) technique typically require supervisory channels (SUPVYs) to facilitate exchange of service information between the nodes of the system. Conventionally, injection of a SUPVY in the WDM system is associated with a generation of a dedicated SUPVY transmission channel outside of the WDM band, incorporation of the SUPVY data in a payload WDM channel, or additional low frequency modulation of the a payload WDM channel with the data of the SUPVY.
However, such means of providing the SUPVY add to already high cost of the fiber-optic components and complexity of modulation and demodulation schemes used in the payload channels of the WDM systems.